This invention relates generally to operational amplifiers, and more particularly, to an operational amplifier utilizing JFET followers each of which is driven by a current source generating a current which is proportional to the saturation current I.sub.DSS of its respective JFET follower and which tracks its respective I.sub.DSS over temperature.
In an operational amplifier which utilizes JFET followers for driving a PNP differential stage, it is desirable that the JFETs be supplied each with a current equal to I.sub.DSS (the drain current when the gate and source terminals are shorted) and in this manner provide a gate-to-source voltage (V.sub.gs) equal to zero and having a temperature coefficient equal to zero (i.e. dV.sub.gs /dT=0). Furthermore, with Vgs on both sides of the amplifier (i.e. V.sub.gs1 and V.sub.gs2) equal to zero, the offset voltage V.sub.os which equals V.sub.gsl -V.sub.gs2 would also equal zero and dV.sub.os /dT would equal zero. Unfortunately, in the past, the required currents equal to I.sub.DSS of the JFET followers could not be assured sufficiently to achieve consistently acceptable results.